i'm not sure if this fits in "Desktop and Multimedia" but as the problem seems to be related to Lightdm, I put it here.

I am running a small network with 10 fat clients. The users authenticate via ldap running on the fileserver for the network. There are no local users defined, only system users. I use lightdm as Display-Manager. Since the update from Wheezy to Stretch, the Greeter does not show the LDAP-Users anymore and the users have to authenticate themselves by typing username and password.

What I mean is: before I updated the clients to Stretch, Lightdm showed me a dropdown-list with users to chose from. LDAP-Users, not local users. After the update, there is no dropdown-list anymore and my users have to type username and password to authenticate. This is only a minor annoyance. But it would be nice to get the list back.